Heroku Amazon s3 images - 403 error sometimes?

I have my server setup at Heroku and i've used Amazon s3 for image-storage (uploaded them with the carrierwave gem), but sometimes i get strange 403 errors:

"Failed to load resource: the server responded with a status of 403 (Forbidden)"

(See image below)

If i reload the page the images are shown again.

I've set up a CORSRule:

 <?xml version="1.0" encoding="UTF-8"?>
    <CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
    <CORSRule>
        <AllowedOrigin>*</AllowedOrigin>
        <AllowedMethod>GET</AllowedMethod>
        <ExposeHeader>ETag</ExposeHeader>
        <MaxAgeSeconds>3000</MaxAgeSeconds>
        <ExposeHeader>Accept-Ranges</ExposeHeader>
        <ExposeHeader>Content-Range</ExposeHeader>
        <ExposeHeader>Content-Encoding</ExposeHeader>
        <ExposeHeader>Content-Length</ExposeHeader>
        <AllowedHeader>Range</AllowedHeader>
        <AllowedHeader>Authorization</AllowedHeader>
    </CORSRule>
    </CORSConfiguration>

I'm not an expert with CORSRule and i tried a few, but i would be so happy if anyone could point me in the right direction.

--------------- Updated --------------

Here i have my Request General, Response Headers and Request Headers when i'm missing an image.

General

Request URL:https://exnerbilleder.s3.amazonaws.com/nye/uploads/image/image/215/thumb_5.jpg
Request Method:GET
Status Code:403 Forbidden
Remote Address:52.95.150.17:443
Referrer Policy:no-referrer-when-downgrade

Response Headers

Content-Type:application/xml
Date:Tue, 08 Aug 2017 15:49:49 GMT
Server:AmazonS3
Transfer-Encoding:chunked
x-amz-id-2:EG4D5X29x8eAuu+xD9PdG2MsdGYnWHnpkuOc87p1h7nbFgvk57S6Be631UwTdF9tHMauoAjf6j4=
x-amz-request-id:0C43705C41CD57C9

Request Headers

Accept:image/webp,image/apng,image/*,*/*;q=0.8
Accept-Encoding:gzip, deflate, br
Accept-Language:da-DK,da;q=0.8,en-US;q=0.6,en;q=0.4
Connection:keep-alive
Host:exnerbilleder.s3.amazonaws.com
Referer:http://inger-exner.herokuapp.com/works/slotsgarden
User-Agent:Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.90 Mobile Safari/537.36

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